So I've been watching through the past seasons of How I Met Your Mother, and last night discovered something very interesting (to me, anyway). The crazy thing is, I can't find any reference to this on the internets... am I the first to notice this??
 
In episode 19 of season 5, the sequences in which Marshall is mugged feature the theme from the first level of Super Mario Bros. 2! It's sped up and played on a piano.  It's not exactly it in this clip, but they play more of the song in other clips. This was the only one I could find. Check out the full episode to hear it.